1. Field of the Invention
The present invention relates to a water dispersion type acryl-based pressure-sensitive adhesive composition which can form a re-peelable pressure-sensitive adhesive layer. More particularly, the present invention relates to a re-peelable water dispersion type acryl-based pressure-sensitive adhesive composition which can form a pressure-sensitive adhesive layer excellent in antistatic properties (peeling antistatic properties), adherability, and re-peelable properties, and also to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer including the above-mentioned pressure-sensitive adhesive composition.
2. Description of the Related Art
In the production and processing processes of an optical member (optical material) represented by an optical film to be used for a polarizing plate, a retardation plate, a reflection prevention plate, etc., for a purpose of preventing scratching and staining on the surface, improving the cutting processibility, suppressing cracks, and the like, a surface protecting film is used while being stuck to the surface of the optical member (see Patent publication 1 and 2). As the surface protecting film, a re-peelable pressure-sensitive adhesive sheet obtained by forming a re-peelable pressure-sensitive adhesive layer on the surface of a plastic film substrate has been usually used.
Previously, solvent type acryl-based pressure-sensitive adhesives have been used as a pressure-sensitive adhesive for surface protecting films (see J Patent publication 1 and 2); however since these solvent type acryl-based pressure-sensitive adhesives contain an organic solvent, it has been tried to replace these solvent type acryl-based pressure-sensitive adhesives with water dispersion type acryl-based pressure-sensitive adhesives from the viewpoint of working environments at the time of application (see Patent publication 3, 4 and 5).
These surface protecting films are required to have sufficient adherability (tackiness) during the time the surface protecting films are stuck to optical members. Further, these surface protecting films are required to have excellent peelable (re-peelable) properties since the surface protecting films are peeled after used in the production process for optical members.
In general, surface protecting films or optical members are made of a plastic material, and thus have high electrical insulating properties and generate static electricity at the time of friction or peeling off. Accordingly, when a surface protecting film is peeled off from an optical member such as a polarizing plate, static electricity is generated and when a voltage is applied to a liquid crystal in the state that the static electricity generated at that time remains as it is, it leads to problems such that orientation of liquid crystal molecules is lost or a defect occurs in a panel.
Further, the existence of static electricity may possibly cause other problems of attraction of dust and waste or deterioration of workability. Accordingly, in order to solve the above-mentioned problems, surface protecting films are subjected to various kinds of antistatic treatments.
Disclosed, as a trial for suppressing electrification of static electricity, is a method for performing antistatic treatment by adding a surfactant with a low molecular weight to a pressure-sensitive adhesive and transferring the surfactant to an object to be protected from the pressure-sensitive adhesive (e.g., see Patent publication 6). However, in this method, the added surfactant with a low molecular weight easily bleeds to the pressure-sensitive adhesive surface and in the case where the method is employed for a surface protecting film, there is a concern of staining of an adherend (an object to be protected).
Further, in use as a surface protecting film (particularly, use as a surface protecting film for an optical member), residue (so-called “adhesive residue”) of a pressure-sensitive adhesive on the surface of an adherend (optical member, etc.) at the time of peeling a pressure-sensitive adhesive sheet becomes a problem, e.g., an adverse effect on optical properties of an optical member, and therefore, a pressure-sensitive adhesive and a pressure-sensitive adhesive layer are required to be excellent in easy peeling properties (re-peelable properties).    [Patent publication 1] JP-A-11-961    [Patent publication 2] JP-A-2001-64607    [Patent publication 3] JP-A-2001-131512    [Patent publication 4] JP-A-2003-27026    [Patent publication 5] JP-B1-3810490    [Patent publication 6] JP-A-09-165460